Graphene is a plane film of sp2-bonded carbon atoms that are densely packed in a hexagon honeycomb crystal lattice, which is a one-atom-thick two-dimensional material, and a thickness thereof is only 0.335 nanometer. Graphene is the thinnest and firmest nanometer material ever known. Graphene is almost transparent, and a light absorptivity thereof is only 2.3%. Graphene has a good thermal conductivity, and a thermal conductivity coefficient thereof is 5300 W/m·K. Graphene has a good electronic conductivity, and an electronic mobility thereof at a normal temperature is larger than 15000 cm2/V·s, while an electrical resistivity thereof is only 10−6 Ω-cm, which is material of a smallest electrical resistivity ever known. Graphene has a high transmittance, a high conductivity, a high flexibility, a high mechanical strength and a high thermal conductivity, which has a great advantage as a transparent electrode of a flexible touch screen and a flexible display product.
At present, a large area of graphene film may be formed by chemical vapor deposition, wherein a graphene is grown on a metal catalytic base material firstly, and then the graphene is moved to a target base material by a proper method. At present, a main target base material is PET film, and a thickness thereof is 100-125 microns. In order to make a flexible touch screen lighter and thinner, a lighter and thinner target base material is needed. At present, polyimide (PI) film is one of the materials forming a flexible display apparatus. The PI film is of a high thermostability, capable of resisting high temperature and of a low thermal shrinkage rate. In addition, a chemical stability, a mechanical stability and an electrical insulation of the PI film are good, especially that a thickness of the PI film may even be 10 to 50 microns (generally 10-30 microns). The graphene may be transferred onto the PI film when the PI film is adopted, so as to form an ultra-thin flexible graphene transparent conductive film. However, if the graphene is transferred by the method in the prior art, a poor conductivity of the transferred graphene, a low yield and a high cost may be resulted due to a deformation of the base material or a process defect, when the graphene is transferred onto an ultra-thin PI film.